Received 16 July 2019; revised 25 October 2019; accepted 31
October 2019
We have reported here the detailed
investigation of the effect of methyl group substitution on
the meta-position of the 2-hydroxypyridine molecule. Resonance
enhanced multiphoton ionization (REMPI), FT-IR and Raman
spectroscopic techniques have been used for the experimental
study of the molecules. Ab initio calculations were
used for theoretical investigations of the molecules. The
origin band of the molecules 3-methyl-2-hydroxypyridine
(3M2HP) and 5-methyl-2-hydroxypyridine (5M2HP) was observed at
33830 and 34105 cm–1 in their REMPI spectroscopy,
and the bands assigned as a ππ* transition state. The
vibronic coupling of nπ* and ππ* transition
states took place in 3M2HP, thus some low intense bands near
the origin band of the molecule were observed in the REMPI
spectrum. However, there was no such kind of bands in 5M2HP.
The π*–σ* hyperconjugation is responsible for
the conformational change of the methyl group in 3M2HP upon
excitation (S0 → S1).
Keywords: methyl
torsion, REMPI, ab initio, hyperconjugation, HOMO, LUMO
PACS: 31.15.A-, 31.50.-x, 33.15.Hp, 32.80.Rm
[1] G.A. Bickel, G.W. Leach, D.R. Demmer, J.W. Hager, and S.C.
Wallace, The torsional spectra of jet‐cooled methyl substituted
indoles in the ground and first excited states, J. Chem. Phys.
88,
1–8 (1988),
https://doi.org/10.1063/1.454636
[2] W.A. Wassam and E.C. Lim, ‘Proximity effect’ and
radiationless transitions in aromatic molecules with non-bonding
electrons, J. Mol. Struc.
47, 129–198 (1978),
https://doi.org/10.1016/0022-2860(78)87184-1
[3] A. Hiraya, Y. Achiba, K. Kimura, and E.C. Lim,
Identification of the lowest energy
nπ* states in
gas‐phase polycyclic monoazines: Quinoline and isoquinoline, J.
Chem. Phys.
81(7), 3345–3347 (1984),
https://doi.org/10.1063/1.447998
[4] G. Fischer and A.E.W. Knight, Narrow band laser excited
fluorescence as a probe of the near-resonance vibronic coupling
in isoquinoline vapour, Chem. Phys.
17(3), 327–342
(1976),
https://doi.org/10.1016/S0301-0104(76)80035-3
[5] G. Fischer and R. Naaman, Near resonance vibronic coupling.
Isoquinoline, Chem. Phys.
12(4), 367–379 (1976),
https://doi.org/10.1016/0301-0104(76)87075-9
[6] P.M. Felker and A.H. Zewail, Jet spectroscopy of
isoquinoline, Chem. Phys. Lett.
94(5), 448–453 (1983),
https://doi.org/10.1016/0009-2614(83)85030-1
[7] A.K. Jameson, B.E. Forch, K.T. Chen, S. Okajima, H. Saigusa,
and E.C. Lim, Electronic and vibrational relaxations in van der
Waals complexes of isoquinoline with argon and nitrogen:
energetics and dynamics of photodissociation leading to S
1
(
nπ*) isoquinoline, J. Phys. Chem.
88(21),
4937–4943 (1984),
https://doi.org/10.1021/j150665a029
[8] R.K. Sinha, B.P. Singh, and T. Kundu, Effect of electronic
states coupling on methyl torsion in 3-methylisoquinoline,
Indian J. Phys.
86(3), 187–194 (2012),
https://doi.org/10.1007/s12648-012-0040-3
[9] A.K. Srivastava, R.K. Sinha, S. Saxena, and T. Kundu, Effect
of methylation on 2-hydroxypyridine in ground state: Theoretical
study, Int. J. Chem. Sci.
16(2), 270(1–13) (2018),
https://doi.org/10.21767/0972-768X.1000270
[10] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria,
M.A. Robb, J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G.A. Petersson, et al.,
Gaussian09 Revision E.01
(Gaussian Inc., Wallingford, CT, USA, 2009),
http://gaussian.com/
[11] A.R. Allouche, Gabedit – A graphical user interface for
computational chemistry softwares, J. Comp. Chem.
32(1),
174–182 (2011),
https://doi.org/10.1002/jcc.21600
[12] R.K. Sinha, B.P. Singh, and T. Kundu, Origin of threefold
methyl torsional potential in methylindoles, Theo. Chem. Acc.
121(1),
59–70 (2008),
https://doi.org/10.1007/s00214-008-0450-7
[13] Y. Matsuda, T. Ebata, and N. Mikami, IR–UV double-resonance
spectroscopic study of 2-hydroxypyridine and its hydrogen-bonded
clusters in supersonic jets, J. Phys. Chem. A.
105(14),
3475–3480 (2001),
https://doi.org/10.1021/jp003272x
[14] M.R. Nimlos, D.F. Kelley, and E.R. Bernstein, Spectroscopy,
structure, and proton dynamics of 2-hydroxypyridine and its
clusters with water and ammonia, J. Phys. Chem.
93(2),
643–651 (1989),
https://doi.org/10.1021/j100339a030
[15] B. Pradhan, R.K. Sinha, B.P. Singh, and T. Kundu, Origin of
methyl torsional barrier in 1-methyl-2(1H)-pyridinimine and
3-methyl-2(1H)-pyridone: II. Ground state, J. Chem. Phys.
126(11),
114313(1–8) (2007),
https://doi.org/10.1063/1.2566602
[16] H. Nakai and M. Kawai,
π*–
σ*
hyperconjugation mechanism on the rotational barrier of the
methyl group (I): Substituted toluenes in the ground, excited,
and anionic states, J. Chem. Phys.
113(6), 2168–2174
(2000),
https://doi.org/10.1063/1.482029